This invention relates to a froth flotation process for the beneficiation of fine coal. More specifically, this invention relates to a froth flotation process for the beneficiation of fine coal using certain polyorganosiloxanes as collectors. The polyorganosiloxane collectors of this invention allow for improved beneficiation of fine coals, especially the difficult-to-float coals including highly oxidized coals.
In general, a froth flotation process for the beneficiation of fine coal occurs as finely disseminated air bubbles are passed through an aqueous fine coal slurry. Air bubble adhering particles (coal) are separated from the nonadhering particles (tailings) by flotation of the coal particles to the surface of the aqueous slurry where they are removed as a concentrate. The tailings or waste remain suspended in the slurry or fall to the lower levels of the slurry. Suitable reagents are normally added to the aqueous fine coal slurry to improve the selectivity and/or recovery of the process. Collectors and frothing agents are two types of additives which are normally used. The basic purposes of a frothing agent is to facilitate the production of a stable froth. The froth should be capable of carrying the beneficiated fine coal until it can be removed as a concentrate. The basic purpose of a collector is to render the desired coal particles hydrophobic so that contact and adhesion between the desired coal particles and the rising air bubbles is promoted. At the same time, the collector should be selective in that the tailings or waste are not rendered hydrophobic and thus do not float. Collectors are generally surface active reagents which preferentially wet or adsorb on coal surfaces and thus enhance the hydrophobic character of the coal particle by giving the coal surface a water repellent coating. Water insoluble, neutral hydrocarbon liquids derived from petroleum, wood, or coal tars have been employed in the froth flotation of coal. Diesel fuel, fuel oil, and kerosene are the most widely used collectors. In specific instances, other flotation reagents may be used. Such additional flotation reagents include depressing agents, activating agents, pH regulators, dispersing agents, and protective colloids which are well known in the art.
Polyorganosiloxanes have been used in mineral flotation processes. Schoeld et al. in U.S. Pat. No. 2,934,208 (issued Apr. 26, 1960) concentrated a coarse sylvite fraction from a sylvite ore using froth flotation with a collector containing both an aliphatic amine and a water insoluble silicone fluid. The silicone fluid employed by Schoeld et al. included dimethyl silicones, phenyl silicones, and methyl hydrogen silicones. Gotte et al. in U.S. Pat. No. 3,072,256 (issued Jan. 8, 1963) discloses the separation of galena and sphalerite present in sulphidic ores by froth flotation using conventional frothing agents and polyorganosiloxanes as collectors where the polyorganosiloxane is in the form of an emulsion with a surface-active nitrogen-containing organic compound. The polyorganosiloxanes of Gotte et al. contained methyl radicals and at least one alkyl radical containing more than two carbon atoms. Smith et al. in U.S. Pat. No. 3,640,385 (issued Feb. 8, 1972) teaches the concentration of sylvite from sylvinite or other potassium chloride ores using a froth flotation system with small amounts of silicone polymers as auxiliary agents in conjunction with primary amines and aliphatic and/or aromatic oils as collectors. The organic radicals on the silicone polymers of Smith et al. included methyl, phenyl, ethyl, propyl, butyl, hydrogen, chlorine, and bromine radicals. Leonov et al., in USSR Inventor Certificate No. 652,974 (Mar. 25, 1979), employed di-[2--(glycidyloxy)ethoxyethyl]ether-1,3-di(oxymethyl)tetra-methyldisilox ane as a frothing agent in the froth flotation of a lead-zinc ore.
Siloxanes have also been used to a limited extent in the froth flotation of coal. Petukhov et al., in USSR Inventor Certificate No. 582,839 (Dec. 5, 1977), employed a mixture of linear and cyclic polysiloxanes of the general formula EQU Si.sub.n O.sub.n-1 (OC.sub.2 H.sub.5).sub.(2n+2)
where n is 2-4 and ##STR1## respectively, as frothing agents for the froth flotation of coal. The collector employed was kerosene. Petukhov et al., in USSR Inventor Certificate No. 650,656 (Mar. 5, 1979) employed polyhaloorganosiloxanes containing methyl, ethyl, --C.sub.6 H.sub.5 X.sub.2, and --CH.sub.2 CH.sub.2 CX.sub.3 radicals, where X is a halogen atom, as frothing agents in the flotation of coal. The collector employed was kerosene. Polydimethylsiloxanes have also been used in the froth flotation of coal with only limited success.
An object of this invention is to provide an improved froth flotation process for the beneficiation of fine coal. Another object is to provide new polyorganosiloxane collectors for use in the froth flotation of fine coal. Other objects will be apparent to one skilled in the art upon consideration of this specification.